1. Technical Field
The present application relates to sensors for aircraft. In particular, the present application relates to weight-on-gear sensors for aircraft with landing skids.
2. Description of Related Art
For a multitude of reasons it is important for various aircraft systems to know if the aircraft is on the ground or in the air. This is referred to in this application as “weight-on-gear” status. For the purposes of this application, “positive” weight-on-gear status means that the aircraft has landed on a surface, and “negative” weight-on-gear status means that the aircraft is airborne. One reason this is important is the desire to disable, or adjust, the operation of weapons systems, or other systems, while the aircraft is on the ground. Because an aircraft may land on a variety of surfaces, it is important that the system used to determine if the aircraft is in flight is not easily damaged, confused, or circumvented by uneven surfaces or unusually high or low friction surfaces.
Some complex systems have been developed to determine whether an aircraft with opposite landing skids is in the air. Some of these systems measure the deflection of one of the cross tubes that connect the landing skids to the fuselage of the aircraft. This sort of system depends on the cross tube and aircraft maintaining tight tolerances over the life of the system. One problem with these systems is that unusually hard landings can deform either the fuselage or the cross tube, making systems that are dependent on this physical relationship unreliable.
Other systems use delicate strain gage sensors on the structural members of the landing gear. The main problem with these systems is that these sensors are easily damaged by harsh environments and therefore not suitable for extended service.
Yet other systems use complex sensors with low tolerances in very limited ranges of operation. Once the range of operation is exceeded, such as by a hard landing or large swing in temperature, the sensor is not able to reliably track further operation of the aircraft.
As might be expected, the above systems may be very expensive either due to initial cost or the high cost associated with frequent maintenance or replacement.